WASHINGTON - Defense Secretary Leon Panetta said he is skeptical of the benefits the Pentagon's propaganda programs provide and added that the military struggles to gauge their effectiveness.

Propaganda can also be dangerous, he said in an interview with USA TODAY, referring to the smear attack against the newspaper by the owner of the military's top propaganda contractor.

"It's always been tough to quantify, frankly," Panetta said. "I've always been a little skeptical about how much good you can get out of that. There are instances where it can serve a purpose, and it can help as a way to defeat our enemies if it's used effectively. I think there are dangers associated with it, that you just have to continue to be very vigilant about, because it can be misused as we saw take place in your area. That's the kind of thing that we just have to be very careful about."

An investigation last year by USA TODAY found that the Pentagon has spent hundreds of millions of dollars on propaganda campaigns in Iraq and Afghanistan, much of it on poorly tracked marketing campaigns that the military refers to as "information operations."

The programs include leaflets and billboards encouraging Afghans to support their government. Millions are also spent on radio and television broadcasts and advertisements whose U.S. sponsorship is often hidden from Afghans because, military officials acknowledge, the information wouldn't be trusted if Afghans knew the source of funding. The Pentagon relies heavily on contractors to produce the propaganda, and has allowed the private firms to grade their own work.

Micah Zenko, a national security expert at the Council on Foreign Relations, a think tank, said the military must inform the public about its actions openly and honestly, not market them through contractors.

"The Pentagon has an obligation to the American people, and the world, to provide information and tell its story - if nothing else to counter myths and misinformation," Zenko said in an e-mail. "But it should only do so in an open and transparent way. Using third-party contractors to shape public opinion is dishonest and unethical."

USA TODAY found that the owners of the top propaganda contractor in Afghanistan, Leonie Industries, had failed to pay $4 million in federal taxes on time despite earning more than $200 million in contracts from the government. Their tax bills were paid after the story was published.

Shortly after USA TODAY made inquiries about the tax bills, fake Facebook and Twitter accounts, as well as phony fan club websites, were set up to disparage USA TODAY reporters. The co-owner of the company, Camille Chidiac, admitted to setting up some of the sites but said he did not use company resources in doing so. He had been suspended from receiving federal contracts because of the campaign, but the military lifted the suspension late last year.

The Pentagon's inspector general has launched a criminal investigation of Leonie and its owners. The company continues its work in Afghanistan.

The Pentagon, meantime, continues to struggle to understand what value its propaganda programs provide, Panetta said.

"Whatever we do, if we're using taxpayer money, I think we've got to be able to show the American taxpayer that we're getting something back for the dollars invested, which means that I've got to be able to quantify what is it we are getting back for the dollars that are spent," Panetta said. "I have to tell you in this area it's tough to quantify."